Hey guys i am posting and replying to things but for some reason i amn't getting activity. why is that?

The activity score only updates "once in a while" (maybe twice a month?), that way there is less load on the server.Good things take time, you will get there.

I THOUGHT it will update every 14 days, so how does it work if its updating every two months, will we skip a position or what

Not every two months it updated on every 14 days , as soon as the activity time starts when you post a single post after 1hrs maximum your account rank updated but according to that your post should also be greater then the rank position. here i post the link where you can find the full deails about the forum activity clear they will explain it.